<template>
     <div class="pagination">
          <button :disabled="pageNo==1" @click="$emit('getPageNo',pageNo-1)">上一页</button>
          <button v-if="startNumAndEndNum.start > 1" @click="$emit('getPageNo', 1)" :class="{active:pageNo==1}">1</button>
          <button v-if="startNumAndEndNum.start > 2">···</button>

          <!-- 中间部分 --> 
          <button v-for="(page, index) in startNumAndEndNum.end" :key="index" v-if="page>=startNumAndEndNum.start" @click="$emit('getPageNo',page)"
               :class="{active:pageNo==page}"
               >{{ page }}
          </button>


          <button v-if="startNumAndEndNum.end < totalPage -1">···</button>
          <button v-if="startNumAndEndNum.end < totalPage" @click="$emit('getPageNo',totalPage)" :class="{active:pageNo==totalPage}">{{ totalPage }}</button>
          <button :disabled="pageNo==totalPage" @click="$emit('getPageNo',pageNo+1)">下一页</button>

          <button style="margin-left: 30px">共 {{ total }}条</button>
     </div>
</template>

<script>
export default {
     name: "Pagination",
     // pageNo: 当前第几页
     // pageSize：代表每一页展示多少条数据
     // total: 代表整个分页一共展示多少条数据
     // continues：代表分页连续页码个数
     props: ['pageNo', 'pageSize', 'total', 'continues'],
     computed: {
          // 计算总共多少页
          totalPage() {
               // Math.ceil向上取整
               return Math.ceil(this.total / this.pageSize)
          },
          // 计算出连续的页码的起始数字与结束数字
          //计算出连续的页码的起始数字与结束数字[连续页码的数字:至少是5]
          startNumAndEndNum() {
               const { continues, pageNo, totalPage } = this;
               //先定义两个变量存储起始数字与结束数字
               let start = 0,
                    end = 0;
               //连续页码数字5【就是至少五页】，如果出现不正常的现象【就是不够五页】
               //不正常现象【总页数没有连续页码多】
               if (continues > totalPage) {
                    start = 1;
                    end = totalPage;
               } else {
                    //正常现象【连续页码5，但是你的总页数一定是大于5的】
                    //起始数字
                    start = pageNo - parseInt(continues / 2);
                    //结束数字
                    end = pageNo + parseInt(continues / 2);
                    //把出现不正常的现象【start数字出现0|负数】纠正
                    if (start < 1) {
                         start = 1;
                         end = continues;
                    }
                    //把出现不正常的现象[end数字大于总页码]纠正
                    if (end > totalPage) {
                         end = totalPage;
                         start = totalPage - continues + 1;
                    }
               }
               return { start, end };
          },
     },
};
</script>

<style lang="less" scoped>
.pagination {
     text-align: center;

     button {
          margin: 0 5px;
          background-color: #f4f4f5;
          color: #606266;
          outline: none;
          border-radius: 2px;
          padding: 0 4px;
          vertical-align: top;
          display: inline-block;
          font-size: 13px;
          min-width: 35.5px;
          height: 28px;
          line-height: 28px;
          cursor: pointer;
          box-sizing: border-box;
          text-align: center;
          border: 0;

          &[disabled] {
               color: #c0c4cc;
               cursor: not-allowed;
          }

          &.active {
               cursor: not-allowed;
               background-color: #409eff;
               color: #fff;
          }
     }
}
.active{
     background: skyblue;
}
</style>